This invention relates generally to pouring of liquid steel, and more particularly to pour tiles for bottom pouring of liquid steel.
The technology of bottom pouring liquid steel was developed in Europe several decades ago. The technology is now employed all over the world at steel plants producing high quality steel grades, such as big forging ingots, bearing qualities, aircraft qualities, etc., to name a few. Prior to this development, liquid steel had been poured from the top into cast iron molds in which the steel solidified into ingots for further processing.
Such earlier techniques exhibited major disadvantages, such as gas pick-up during pour, poor ingot surface, poor internal cleanliness, segregation, reduced ingot yield, etc. Those drawbacks have effectively been eliminated by the use of bottom-pour technology.
As is known in bottom-pour technology, a series of refractory, hollow-wear shapes, such as trumpet bell bricks, center risers, spider bricks, runner bricks and gate bricks are set up. The refractory bricks are tightly gripped in cast iron sprue plates and cast iron flumes. Any space between the hardware and the refractory material is filled with sand, or another appropriate filler material. In fact, it has been a standard practice to mortar the joints between the different refractory bricks in order to form a sealed tubular system that allows the liquid steel to be poured therethrough without leakage.
After the bottom-pour system is set up, an activity undertaken with great care, liquid steel is poured from a steel ladle into the trumpet bell. The liquid steel flows through the refractory bottom-pour system and fills up the molds from the bottom to the top. Obviously, any leakage in the system has the potentially disastrous effect of the liquid steel breaking out. In such a case the whole heat may be lost if such an accident occurs. Moreover, persons in the area may become injured.
Currently, all bottom-pour refractory bricks have been supplied with cooperating male/female joint systems. The bricks each include a central passageway for the liquid steel to pass therethrough, with the central passageway having a longitudinally extending central axis. Each brick includes at least one male portion or "tongue" projecting outwardly from one end thereof and surrounding the central passageway, while the other end of the brick includes at least one correspondingly shaped "groove" surrounding the central passageway. In particular the tongue of any brick is in the form of an annular flange having an external face which extends at approximately 30.degree. to the longitudinal central axis of the brick and at approximately 60.degree. to the brick's end face ("shoulder"). The groove of any brick is a correspondingly shaped annular recess having a sidewall which extends at approximately 30.degree. to the longitudinal central axis of the brick and at approximately 60.degree. to the brick's end face. Typically the height of the tongue, i.e., the distance between the end face of the tongue and the shoulder from which the tongue projects, is approximately 10 mm, and the depth of the groove, i.e., the distance between the bottom of the groove and the shoulder into which it extends, is approximately 8 mm. Accordingly, when the tongue of one brick, e.g., a runner, is disposed within the groove of another brick, e.g., a sprue, so that the end face of the tongue abuts the bottom surface of the groove a gap of 2 mm thickness is created between the sidewall portions of the tongue of the runner and groove of the sprue and also between their adjacent shoulders. It is in this space or gap that mortar is applied to seal the joint.
In modern steel making practices, especially in North America, the bottom-pour refractory brick designs as described immediately above have been modified to effectuate faster bricking or assembly of the shapes by the elimination of the necessity for utilizing mortar at the joints. To achieve that end, the bottom-pour bricks or tiles were modified to reduce the joint tolerances as much as possible so that there would be a good sealed interface therebetween to prevent steel leakage at the interface even with no mortar between the joints. While such an approach has the advantage of eliminating the need for mortar it nevertheless suffers from various major disadvantages. In this regard, at present almost all bottom-pour tiles are manufactured by what is known as the "stiff-mud process". This process, by its nature, does not allow for the creation of tight tolerances in the manufacture of the bricks because the brick dimensions change from the initial green stage through the firing process of the bricks in the kiln. Accordingly, the bricks are approximately 4-6% smaller after the firing process, so that consistency of tight tolerances is impractical. Moreover, since bottom-pour refractory tiles are a consumable product, that is are used for only one application, the cost of manufacturing is a significant factor, thus the tiles must be inexpensive to manufacture in order to provide a product at a competitive price, notwithstanding the fact that the device may be cheaper to install. As an alternative to the "stiff-mud process" certain refractory suppliers, e.g., the Japanese, have begun developing a dry pressing process to manufacture bottom-pour bricks. Such a procedure allows for very narrow or tight refractory tolerances for the bricks to enable a tight fit between the male and female members, i.e., the tongue and the groove at the shoulders of the joint, so that an almost leak-proof joint is provided. However, bottom-pour tiles produced by the dry pressing process are significantly more expensive as compared to bricks or tiles made by the stiff-mud process. In fact the cost factor of two to three times the cost of bricks made by the stiff-mud process is not uncommon with the dry pressing process. Obviously such substantially higher manufacturing costs adversely affect the economics of bottom-pour technology.